Heretofore, a zone type mobile communication system included a zone switching operation that provided communications for the ordinary automobile telephone system by utilizing a plurality of mobile radio base stations to detect the received levels of radio waves transmitted by the mobile stations. A mobile control station, according to the received levels transmitted by the mobile radio base stations, selects the mobile radio base station of which the received level is highest.
This will be described in more detail. A given mobile radio base station monitors the received level of radio waves transmitted by a predetermined mobile station, and when the received signal level becomes lower than a predetermined value, assumes that the mobile station of interest has entered another zone; the base station then transmits a level deterioration signal to the mobile control station. Upon reception of the level deterioration signal, the mobile control station commands the remaining mobile radio base stations to monitor the signal levels of the mobile station of interest. The mobile control station compares the signal level of the mobile station as reported by each of the mobile radio base stations and selects the base station reporting the highest received signal level from the mobile station of interest. The mobile control station then assigns a new channel between the mobile base station so selected and the automobile switching center, and instructs the previous mobile radio base station to disconnect its channel.